1. SISSA/ISAS - International School
for Advanced Studies, Trieste 34136, Italy
2. Computational Biophysics, German
Research School for Simulation Sciences, D-52425 Jülich, Germany
and Institute for Advanced Simulation IAS-5, Computational Biomedicine,
Forschungszentrum Jülich, D-52425 Jülich, Germany
3. Department of Chemistry and Department
of Biochemistry, University of Washington, Seattle, Washington 98195-1700,
United States